Obviously, he's not saying they all have to be LD as he's hired a number of LDS coaches over his tenor as Head Coach. I think what he is saying (reading between the lines), is that they do need work in and support the overall mission of BYU. This would include them living the honor code as the players need good examples. They also will need to encouraged players to live the honor code, go on missions, do well academically, etc. I don't think it's too hard to understand that there aren't many non-LDS coaches that would be willing to do this particularly for any meaningful length of time.